This proposal addresses the need to develop a new class of magnetic resonance (MR) contrast agents, Trimetaspheres for dynamic contrast MR imaging in small animal studies. Dynamic contrast focuses on the use of contrast agents of different molecular sizes having different abilities to penetrate into tumor and normal tissue. Such contrast agents can be used to highlight differences between normal and abnormal tissue, highlight the vascular supply of tumor tissue, and may have important prognostic implications for tumor growth, metastatic potential and aggressiveness. Luna Innovations will manufacture an appropriate Trimetasphere nanomaterial (such as Gd3N@C80) and functionalize it with polyethylene glycol of different molecular sizes to obtain preliminary data to assess the ability of these novel nanomaterials as potential dynamic contrast agents. Preliminary studies using normal mice will be pursued in a 4.7T MR scanner specially designed for small animal imaging through our collaborators in the Biomedical MR Laboratory at Washington University. Key issues to be characterized in vivo include how fast the agent remains in the blood stream, how fast it penetrates into normal tissues, and how soon it is excreted through the kidneys. Phase I results will establish a baseline to study a metastatic cancer model in Phase II.